Since the first synthetic absorbable suture made from braided multifilaments of poly(glycolic acid) was introduced in about the year 1970, advancements in the design and synthesis of bioabsorbable polymers have resulted in continuous improvements in absorbable suture products.
In addition to the suture application, high strength, highly flexible, tough, and durable fibers that possess a prolonged flex fatigue life are needed for use as braided, knitted, woven, or non-woven implants to augment and temporarily reinforce autologous tissue grafts or to serve as scaffolds for tissue regeneration. One example of such an implant is known as a ligament augmentation device (LAD) used to reconstruct the anterior cruciate ligament (ACL) of the knee. Bioabsorbable fibers of the prior art, such as poly(L-lactic acid) (PLA), have not been successful in this application due to low flex fatigue life, shedding of wear debris due to the brittle nature of the fibers, and prolonged bioabsorption time.
Other well known uses for bioabsorbable polymers that have not been fully realized or perfected with available polymers of the prior art include scaffolds for tissue engineering, bioabsorbable knitted vascular grafts, drug-releasing devices, growth factor-releasing implants for bone and tissue regeneration, and fiber-reinforced composites for orthopedic applications. For example, composites of polymers reinforced with dissimilar materials, such as dissolvable glass fiber reinforced poly(lactic acid) are unacceptable for use as implants, the following reasons. Although dissolvable glass fibers provide high modulus needed for the composite to have high initial strength and stiffness, adhesion between glass and polymer invariably fails prematurely in vivo resulting in devices with unacceptable in vivo performance.
Self-reinforced composites were developed as an alternative to composites of polymers reinforced with dissimilar materials, such as those described above. In self-reinforced fiber composites both reinforcing fibers and matrix are made of the same material. Although the stiffness is lower than can be achieved with glass fibers, this alternative type of composite ensures good adhesion between fiber and matrix and thus offers the possibility of longer lasting in vivo strength. Self-reinforced poly(glycolic acid) (PGA) rods, pins and screws made by hot pressing or sintering PGA fibers have shown promise in clinical use. The main disadvantage of PGA in general is that it degrades too fast for orthopedic applications and releases an excessive concentration of acidic degradation products into the surrounding tissue.
Despite the advancements in the art of producing polymeric materials and methods for making polymeric materials suitable for use in sutures, molded devices, and similar surgical devices. Specifically, there continues to be a need for new fibers that are monofilament, have high initial tensile knot strength, retain useful strength in vivo for about two weeks or longer, are fully bioabsorbed within a few months after strength loss, and have very low bending stiffness.